To date, there has been known a valve timing control device including a drive side rotating member that rotates in synchronization with a crankshaft and a driven side rotating member, disposed so as to be rotatable relative to the drive side rotating member, that rotates together with a camshaft (for example, refer to JP 2012-92722A (Reference 1)).
JP 2012-92722A (Reference 1) discloses a hydraulically-driven variable valve device (valve timing control device) including a housing (drive side rotating member) that rotates in synchronization with a crankshaft, a vane rotor (driven side rotating member), disposed so as to be rotatable relative to the housing, that rotates together with a camshaft, and a holding mechanism (locking mechanism) that locks the relative rotation phase of the housing and vane rotor at a phase (lock phase), positioned between a most retarded phase and a most advanced phase, appropriate to starting up an engine. The holding mechanism of the hydraulically-driven variable valve device is configured so as to, utilizing a flip-flop action of the vane rotor due to camshaft torque fluctuation (alternating torque), cause the relative rotation phase of the housing and vane rotor to reach a lock phase appropriate to starting up the engine from the most retarded phase, while regulating in steps by causing a pin (regulating body) to engage sequentially with a plurality of stepped portions, when starting up the engine. In Reference 1, of relative rotations θ1 to θ4 of a first step relative rotation (a first relative rotation from the most retarded phase to a first stepped portion) θ1 to a last step relative rotation (a last relative rotation from a penultimate stepped portion to a last stepped portion) θ4, the last step relative rotation θ4 is set to be the smallest.
However, as the hydraulically-driven variable valve device (valve timing control device) of Reference 1 is such that the last step relative rotation θ4 is set to be the smallest, the relative rotations θ1 to θ3 of the steps before the last step are relatively large in comparison with the last step relative rotation θ4, because of which, the amount of vane rotor flip-flop necessary in order to cause the pin to engage with the stepped portions corresponding to the steps before the last step increases commensurately.
Herein, the amount of vane rotor flip-flop due to the camshaft torque fluctuation has a tendency to be small immediately after cranking is started (in an initial cranking stage shortly after cranking is started), and to subsequently increase gradually. That is, when starting up the engine, hydraulic oil for regulating the relative rotation phase by hydraulic pressure when the engine is operating being loaded in a hydraulic chamber configured by the vane rotor and housing, the loaded hydraulic oil is gradually discharged, utilizing the camshaft torque fluctuation, when the engine is started up.
As the amount of vane rotor flip-flop gradually increases from the small condition immediately after cranking is started (the initial cranking stage), as heretofore described, it may happen that the amount of vane rotor flip-flop at a step (for example, the first step or second step) before the last step is not sufficiently large. In this case, when the amount of flip-flip necessary in order to cause the pin to engage with the stepped portion corresponding to a step before the last step is large, as in the hydraulically-driven variable valve device of Reference 1, time is needed for the pin to engage with the stepped portion corresponding to the step before the last step, because of which, time is needed to bring the relative rotation phase nearer to a lock phase appropriate to starting up the engine from the most retarded phase, as a result of which, there is a problem in that it is not possible to cause the relative rotation phase to swiftly reach a lock phase appropriate to starting up the engine.
A need thus exists for a valve timing control device which is not susceptible to the drawback mentioned above.